1. Field of the Invention
The present invention relates to a gas turbine combustor of a low NOx (nitrogen oxide) emission type and a combustion control method thereof of a gas turbine including a jet engine, an industrial gas turbine or the like.
2. Description of the Prior Art
FIG. 3 is an explanatory view showing a schematic structure of a prior art gas turbine combustor of a low NOx emission type.
In FIG. 3, numeral 1 designates a combustor case and numeral 2 designates a diffuser, through which supplied air pressure is recovered and flow distortion is decreased. Numeral 3 designates a fuel injector, numeral 4 designates a swirler, that swirls the inflow air and numeral 5 designates a liner, in which dilution port(s) 6 and cooling slits 7 are provided.
Numeral 8 designates a bypass duct, that is provided in the liner 5. The air that has passed through the bypass duct 8 is not supplied into a primary combustion zone 9, that is shown being surrounded by a broken line in FIG. 3, but is led to a combustor outlet. This means that the more air that passes through the bypass duct 8, the less air that is supplied into the primary combustion zone 9 via the swirler 4.
Numeral 10 designates a bypass duct variable valve, that is provided in the bypass duct 8. An actuator 11 is provided on the outside of the combustor case 1 and the bypass duct variable valve 10 is operated by the actuator 11 so as to open and close the bypass duct 8.
Thus, by operating the actuator 11, quantity of the air to be supplied into the primary combustion zone 9 via the swirler 4 can be adjusted.
In the prior art gas turbine combustor constructed as mentioned above, if a gas turbine operation condition (including load condition) is decided, the NOx emission quantity is decided by a local fuel-air ratio (or local equivalent ratio) in the primary combustion zone 9. The local fuel-air ratio is decided by the ratio of flow rate of fuel injected from the fuel injector 3 to flow rate of air supplied through the swirler 4.
FIG. 4 is a performance curve showing a relation between the local fuel-air ratio in the primary combustion zone and the NOx emission quantity.
As understood from FIG. 4, if the local fuel-air ratio is reduced, the NOx emission quantity can be reduced. But if the local fuel-air ratio is reduced beyond a limiting value, flames come within a blow-off area as shown by hatching and there arises a problem in that the combustion efficiency lowers or blow-out is caused. Hence, in order to reduce the NOx emission quantity, the local fuel-air ratio is usually reduced to within the range that causes no such problem.
That is, in the prior art, control of the local fuel-air ratio is done such that the actuator 11 is operated to thereby operate the bypass duct variable valve 10 so as to control the air quantity to be supplied into the primary combustion zone 9 via the swirler 4. However, the combustor case 1 is usually heated to about 600° C. and the liner 5 to about 900° C. and hence sliding portions of the components of the air quantity control mechanism that operate in such high temperature portions are liable to cause sticking, biting, etc., which often leads to a large damage to the reliability of the design of the device.
Also, in the portion where the actuator 11 is provided passing through the combustor case 1, there is inevitably provided a clearance to some extent. Hence, high pressure air leaks therethrough and there arises a problem that the efficiency lowers to that extent.